The present invention relates to packages for semiconductor devices, and more particularly to an improved base for a semiconductor package that electrically isolates the package from the heat sink on which it is mounted and that provides low thermal resistance.
With reference now to FIG. 1, prior art packages 10 for semiconductor devices typically include an encapsulant 12 enclosing and protecting a semiconductor device (not shown) to which are attached one or more leads 14 (e.g., gate, source and drain; anode and cathode), with the number and type depending on the semiconductor device enclosed within the package 10. The package 10 may be attached by conventional means 16 to a heat sink 18 for conveying away heat generated by the semiconductor device. The package 10 may be electrically isolated from the heat sink (and thus from other packages carried by the heat sink 18) by an insulator 20 that also is thermally conductive, such as mica. The bottom of the package 10 desirably has high thermal conductivity to facilitate conveyance of heat from the semiconductor device. To this end, the bottom of the package 10 has typically been a thermally conductive metal that is usually also electrically conductive, such as copper; hence the need for the insulator 20 to isolate the package 10.
As is apparent, the insulator 20 adds cost and complexity to the package mounting problem, and is desirably eliminated. But the insulator could not be eliminated so long as the package, and particularly its bottom, was an electrically conductive material.
It is also apparent that the package, particularly the one illustrated in FIG. 1, can only have a limited number of electrical leads 14 extending from the side of the package. Further, the side mounted leads make the placement of multiple semiconductor devices within the package particularly difficult. This is especially apparent in view of the commercially standardized shapes and sizes of the packages (e.g., the TO-xxx family of standard packages). The standard shapes and sizes limit flexibility in selecting which multiple semiconductor devices may be used, forcing uneconomical compromises in numbers and types of devices.
In part because the leads 14 extend from the side, it has been customary to connect the leads 14 to the semiconductor device with wire that is bonded or soldered to the device and to the lead. These attachment methods may increase impedance and consume valuable real estate.
Accordingly, it is an object of the present invention to provide a novel package and method of packaging semiconductor devices that obviates the problems of the prior art without increasing complexity or cost.
It is another object of the present invention to provide a novel package and method of packaging semiconductor devices that electrically isolates each package from the heat sink and provides low thermal resistance.
It is yet another object of the present invention to provide a novel package and method of packaging semiconductor devices in which the package base is an electrical insulator, such as AlN, BeO or pressed diamond.
It is still another object of the present invention to provide a novel package and method of packaging semiconductor devices in which the package base is an electrical insulator that is supported by a thermally conductive support.
It is a further object of the present invention to provide a novel package and method of packaging in which an electrically conductive foil is affixed to an insulative base for the package and to which the semiconductor devices are affixed.
It is yet a further object of the present invention to provide a novel package and method of packaging semiconductor devices in which a conductive foil affixed to an insulative base and electrode leads extending from the semiconductor devices have portions that extend vertically so that multiple semiconductor devices may be placed in the package.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.